Method of inhibiting hydrogen sulfide corrosion of metals



Patented July 8, 1952 METHOD OF INHIBITING HYDROGEN SULFIDE CORROSION OFMETALS Melvin I. Moyer, Lawrence, Kans., and Joseph M. Hersh, ForestHills, N. Y., assignors to'Cities Service Oil Company, Bartlesville,kla., a corporation of Delaware No Drawing. Original applicationSeptember 11, 1947, Serial N0. 773,506. Divided and this application May10, 1949, Serial No. 92,506

Claims.

, 1 Our invention relates to an improved method of inhibiting corrosionof metal, and is more particularly concerned with the treatment ofhydrogen sulfide containing brines of the type obtained in theproduction of crudeoil to reduce their corrosive efiects upon oilproduction and transmission equipment; o

This application is a division ofour copending application Serial No.'77 3,506, filed September 11, 1947, now U. S. Patent No. 2,496,354.

The corrosive action of oil fieldbrines containing hydrogen sulfide insolution ha long been recognized as a source of very substantial lossesin oil production equipment. In some fields, for exampleythe brinewhichis-taken outwith the oil is so corrosive in its nature asto b capable ofdestroying the well tubing within a matter of a very few months; andthewell casings, separators, pumps, and other equipment with which suchmixtures come into contact has a comparably short life. It .has been thepractice to utilize caustic soda, soda ash, and other alkaline compoundsfor neutralizing theacidic components of brines of this generalcharacter, and of thereby limiting their corrosive action: Theseneutralization treatments, however, require the use of comparativelylarge amounts of the inhibiting agents, are correspondingly costly, andfrom a long range point of view, have not been outstandingly successful.

The primary object of our invention is to provide an improved processfor protecting metals, and particularly iron and steel equipment, usedin the handling of crudeoil in the presence of the highly corrosivetypes of'brines frequently encountered in oil fields.

We have discovered that oil well tubing and casings, as well as otherequipment used in oil production, may be sunbstantially and efiectivelyprotected against corrosive action of connate brines by mixing with thelatter, an organic amino-reactive compound which serves as acorrosion-inhibitor. In general we have found that the heterocyclicamino-reactive compounds, the alkyl and alkanol amine-aldehydecondensation products of bothcyclic and noncyclic types, andthe-alkyl-ureas are effective for our purposes.

In accordance with our invention we inject a suitable quantity of aselectedinhibitor compound into an oil .wellandtherebyimingle it withthe oil-brine production sothat the, mixture comes into contact with thewell tubing, casing, and other producing equipment. Thus w may duce theinhibitorinto the top of the casing so that it flows down into thewelland thence back through the tubing, pumps, collecting lines, etc. Ingeneral we have found that this procedure suflices to protect the entiresystem of production and collection against corrosion, to a verysubstantial degree; and far more efiectively than treatment with causticand other inhibiting compounds which have heretofore been used. Whileintroduction of the inhibitor at the wellhead usually suflices, as hasbeen indicated, it will be obvious that the selected compound may beadded to an oil-brine mixture'at any point in a system where itspresence is required to limit corrosive, action. It will further benoted that we prefer to introduce the inhibitor, in liquid form, as anaqueous or alcoholic solution for example, for' greater convenience inhandling and so that it' may more readily mix with and dissolve in thebrine to perform its intended function.

The effectiveness of our inhibitors may be bet-- ter and more easilyunderstood by reference to certain tests which we have conducted uponnatural oil field brines containing approximately 40,000 parts permillion (by weight) of natural saline solids and about 1,000 parts permillion (by weight) of hydrogen sulfide, an analysis. which is typicalof corrosive brines produced in many fields. The test procedureinvolved'the measurement of the corrosive action of this brine, aloneand with our inhibitor compounds, upon thoroughly cleaned and polishedstrip of cold rolled steel measuring! x inches x 16-18 gauge underconditions which closely approximate those existing in a producing oilwell. n In carrying out the tests, we filled a series of 16 :ouncebottles with natural gas in order to. exclude. air, and to each added acalculated quantityofone ofiour' amine reactive inhibitors, and then. ameasured quantity of brine to ake up the inhibitor mixture, followingwhich ates! strip of known weight was completely immersed'inthe mixtureand the bottles were sealed with rubber stoppers to insure an airtightsystem. .Additional tests were run in other bottles in which the weighedtest strips were immersed inzuninhibited brine, that is, in the hydrogensulfide containing brine just as taken from an oil well. All of thetests were run in multiple, both for the inhibited and the. blanksolutions, in order to avoid theanomalies of testing. At the end of atest periodof abouttwo weeks, the

test strips wereremoved from;the-bottles,'rinsed with water, and werethen dipped in l; per cent hydrochloric acid solution for ten seconds toremove any light or. acid washable film, following which theyweresuccessively rinsed in water, dried and weighed to determine theamount of metal lost in the corrosion treatment.

In several series of tests carried out in the manner describedaboveitwas observed that uninhibited corrosion weight loss in different brinesvaried fromibd'ut' 20mg. to over 170 mg. per test strip while the weightloss of strips subjected to the same brines containing our inhibitorswere sharply less. These test data were, used to determine theprotection numbers, i. e., the ratio of loss of weight of a stripsubjected to an uninhibited brine to the loss of weight, of a stripsubjected to the same brine containing our inhibitor, which are reportedbelow in the third column of Table I. For purposes of comparison, wethen assumed a weight loss of 100 mg. for the uninhibited strip test,and corrected the actual weight losses suffered by the test stripssubjectedto the inhibited brines to this assumed basis, thus give ingthe several weight losses set forth in the fourth column or the table.

The results'fofthe'se tests clearly indicate that our. variousihhibitorshave a marked effect in reducing metal loss by the corrosiveaction of hydrogen sulfide containing brines. Since these tests were.carried out under conditions closely approximating those existing in'actual wells, they demonstrate the inhibiting effect which theagents-have in protecting] oil well tubing, etc.,

under actual producing conditions.

. freeze.

I 3 I Inhibitor lirotee I Weight V Inhibitor j v Ooncention Loss MilliaI V- 1 tration Number grams (1 1 nlidgctionproduct of diethanolamine;(2.m01s) and formaldehyde mlllida ction product-of ethylene diamine (1mol) and formaldehyde R ee it tion product of monoethaiiolaminefd mol)and formaldehydellmoDu It will be observed that the foregoing series oftests were carried out 'in solutions containing 62' -parts-of inhibitorcompound per millon parts of brine, thus giving a basis for-evaluatingthe effectiveness or one' inhibitor with respect to another Theprotecting effectiveness'of any of these agentsma'y- 'be varied,however, by increasing'or'decreasing the amount employed inthe.treating-:process.

' Itimay bernoted that brines taken from different wells,i.eventhoughcontaining about the same concentrationof salt and hydrogen sulfide,maybe; moreor less destructive} in their effects upon oil handlingequipment. In using our inhibitors, therefore, we find it desirable toadjust the proportionemployedin accordance with the corrosive characterof the brine under treatment. As a generalrule, wefind that fromabout15-to 250parts (by weight) of inhibitonper'million parts"'(by' weight) ofbrine, is suiiicient to assure highly satisfactory protection undernormal op erating conditions. I I

At the conclusion of the foregoingtests, and others which need not bespecifically considered, it was observed that the metal strips exposedvto the uninhibited brines were coated with a thin, fiuocculent,raytorblack material. Doubtless this coating has some effect inprotecting the underlying metal and slowing down corrosive action. Itcannot be of any great protection value, however, because of itstendency to flake off as is evidenced by the fact that the uninhibitedbrines were turbid with agrayish flocculent precipitate, even lthoughthey had been standing in'a quiet statefor approximately two weeks. Byway of contrast, the metal strips subjected to the brines containing ouraminoreactive inhibitors developed thin but highly tenacious coatingwhich appear to be particularly resistant to hydrogen sulfide brinereaction.

' Some; evidence of the resistant character of these films is tobeij'found in the fact that a tenminute treatment in 1 per centhydrochloric acid did not effect complete removal in many cases, andthat they were not immediately affected by organic solvents such asalcohol, acetone, ether,

methyl ethyl 'ketone, gasoline, benzene, toluene, carbon tetrachloride,-and similar solvents.

The inhibiting action of the amino-reactive compounds is not fullyunderstood: but one aspect of the action, and thesuccessful protectionof metal against substantial corrosion, certainly appears to lie in theformationof a protecting film upon the metal, as described above. Thesefilms may be complex organic products developed by the action of theinhibiting agent or its inter-v action with a portion of the hydrogensulfide and brine, in the presence of metal. They certainly are not theresult of mere neutralization of the hydrogen sulfide, as'is evidencedby' the presence of a high concentration .of that ingredient in thetreated brines. It may be pos activity of the hydrogen'sulfide, andother cor.-

rosive constituents of the brine. 'Whatever thenature'of the action maybe, these facts remain clear: A film is built up on metal surfacesbrought into contact with hydrogen sulfide containing brines which havebeen treated with amino-reactive compounds in accordance with ourinvention; and those films are resistant both to mechanical abrasion andchemical reaction; and that thepresence of the compounds in such brinesdoesvery materially inhibit corrosion: of well tubing, casings, and.other oil field equipment carrying the treatedfbrines.

It will be' observed thatv the inhibitor com: pounds are readilyobtainable in high concentration, which permits economical shipment andhandling both in'transit and in the field.

It is tobe understood that our improved process is not confined to the'use of only one ofthe inhibiting compounds referred to but the variousmixtures of the inhibitors inay be used in a single new and useful'is:

The o ss P v nt n -Pangaea sit-metal x e to We rin s gn ein ng e re iver, 2 p nd v w h. cempri e n roducing, into thebrine, at thegwell bottom,a.'small;.pro-

portion of diethyl thiourea an'd.thereafter c'ausing the brineJcontainingth'emethyl-thiourea to flow in contact with the metalsurfaces te be pro-' tected. 7 r 2. The process according to claim whichdiethyl thiourea is incorporated in the brine in'the amount of fromabout 15 to about 250 parts by weight of diethyl thiourea per millionparts by weight of brine.

3. The process of protecting metal equipment which is subject to thecorrosive action of oil well brines containing hydrogen sulfide whichcomprises introducing into a petroleum-brine mixture containingcorrosive sulfur compounds. at the well bottom, a corrosion inhibitingagent consisting essentially of diethyl thiourea, and thereafter causingthe brine containing the diethyl thiourea to flow in contact with themetal equipment to be protected.

4. The process according to claim 3 in which diethyl thiourea isintroduced into the oil in an amount of from about 15 to about 250 partsby weight of diethyl thiourea per million parts by weight of the brineassociated with the oil.

5. The process of inhibiting the corrosion of metal equipment whenexposed to corrosive brines containing hydrogen sulfide, which comprisesintroducing into the brine, at the well bottom, a

6 small proportion of diethyl thiourea, the proportion of diethylthiourea being efiective to substantially inhibit the corrosion of metalequipment, and thereafter causing the brine containing the diethylthiourea to flow in contact with the metal equipment to be protected.

MELVIN I. MOYER. JOSEPH M. HERSH.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

1. THE PROCESS OF PREVENTING CORROSION OF METALS EXPOSED TO OIL WELLBRINES CONTAINING CORROSIVE SULFUR COMPOUNDS WHICH COMPRISES INTRODUCINGINTO THE BRINE, AT THE WELL BOTTOM, A SMALL PROPORTION OF DIETHYLTHIOUREA, AND THEREAFTER CAUSING THE BRINE CONTAINING THE DIETHYLTHIOUREA TO FLOW IN CONTACT WITH THE METAL SURFACES TO BE PROTECTED.